The present invention relates to a musical envelope control device, and, more particularly, to a musical envelope control device which is employed for an electronic watch device which produces melody sounds at a predetermined time and which controls the envelope characteristics of the melody sounds.
Recently, digital electronic watches which play various melodies instead of a monotonous alarm sound at predetermined times have become commercially available. These digital electronic watches display the time digitally, and a desired time may be set by the user. A conventional electronic watch with a melody function comprises a memory circuit for storing pitch data and duration data of a melody, a pitch frequency divider and a duration frequency divider which respectively produce a pitch signal and a duration signal according to the pitch data and the duration data, an address counter for specifying a memory address of melody sound data which is stored in the memory circuit, and a speaker means for converting an electric signal to a sound signal, in addition to a known timing circuit. An impedance circuit, corresponding to an envelope waveform producing unit, is further provided for improving the tone quality of the melody produced by a conventional electronic watch to be as real as possible. The impedance circuit, for example, is constituted by a parallel circuit of a capacitor and a resistor. The potential of a melody signal is controlled in accordance with a time constant determined by the capacitance of a capacitor C and the resistance of a resistor R. A continuity characteristic (called a "Release" waveform) is added to the melody signal so that a melody sound having the desired envelope characteristic is produced.
In an electronic watch having an impedance circuit as the conventional envelope waveform shaping unit, only a leading-edge continuity characteristic (Attack-Release characteristic) is accomplished. The envelope waveform of a sound made by a natural musical instrument at the peak of the waveform substantially consists of a leading edge portion (to be referred to as an Attack hereinafter), a trailing edge portion (to be referred to as a Decay hereinafter), a constant portion (to be referred to as a Sustain hereinafter), and a continuous portion (to be referred to as a Release hereinafter). Therefore, a melody which is generated by the conventional electronic watch and only has the Attack-Release characteristic sounds different from a natural sound because of an unnatural tone quality. A waveform of the Release (continuity time) which is added to the melody sound is determined only by the time constant of an impedance circuit. Therefore, a predetermined constant Release waveform is added to the melody sound independently of the tempo of the melody. As a result, an envelope characteristic which corresponds to the tempo of the melody, that is, to the performance speed, cannot be obtained. For example, when the time constant of the impedance circuit is set at a general melody tempo, a melody with an up-tempo may not be produced with clear tone. To the contrary, if the time constant of the impedance circuit is set for a fast tempo, a melody with a slow tempo is interrupted, degrading the tone quality.